Hide your doubts, smile and act confident and you'll be OK most of the time...
..but when it fails it can lead to disasters, especially if entire teams are engaging in this behavior.
However, don't exaggerate or emphasize them too much either, but rather get in the mindset of wanting to become better at the skill/subject, and display that mindset.
I'd think much higher of a person who did that than someone who pretends everything is fine when they are struggling. Also, if you display this mindset, people will offer to help you, too!
do you have any examples of this?
They have to make a lot of pieces fit together that all converge to a solution at the right time to keep everything overall moving, and can't do that without good information.
It's more important to the company that the project get done than that you did it all by yourself, and if you're afraid to disclose your barriers or doubts then it will fail spectacularly. You will look infinity times worse failing to meet a deadline without advance warning than if you go to your boss a month before and explain that the problem has <x, y, and z> unexpected issues and that you need help.
"Yeah, I know, I’m so scared. When Lawrence offered me this job, I was so worried about whether I could do it. I mean it’s all so complicated, and the connections to be made over the network are so uncertain, and then, everything, the timeouts, the servers, lost messages, everything I have to think about it, it’s just really overwhelming and scary, you know?"
It sounds like a lack of confidence. However, Deborah Tannen has suggested a different interpretation.